Disposable filter cartridges having longitudinally pleated filtration media are well known. In this regard, disposable filter cartridges are conventionally provided with an external cylindrical cage and a central core element coaxially positioned within the cage so as to define an interior cylindrical annulus which is completely occupied by the pleated filter media. Please see generally in this regard, U.S. Pat. Nos. 5,145,827 to Ashelin et al, and 4,154,688 to Pall (the entire content of each being expressly incorporated hereinto by reference). The cage and the core element are provided with openings, apertures and the like so as to allow fluid to flow normally in a radial direction through the external cage, pleated filter media and core element in that order. The filtered fluid may then be discharged axially from the filter cartridge through a coaxially disposed discharge opening in one of the filter cartridge's end caps.
In some industrial environments, it may be desirable to reverse the normal flow of the fluid through the filter cartridge so as to dislodge and remove accumulated particulates on the surface of the pleated filter media so that the filter cartridge substantially (if not completely) regains its initial filtration capabilities and/or so that fresh particulates may be precoated onto the filter media's surface. For example, in some industries (e.g., the power generation industry), filtration cartridges having filter media precoated with ion exchange particles are sometimes used. Thus, it would be desirable if exhausted ion exchange particles could be removed from the filter media via back-flushing so that fresh ion exchange particles could then be recoated onto the filter media's surface. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is directed to a back-flushable disposable filter cartridge. More particularly, the present invention is embodied in a filter cartridge whereby a generally cylindrical, longitudinally pleated, filter media is positioned within the external filter media cage such that an annular space is defined therebetween. The annular space also serves to prevent blockage of particulates from occurring (e.g., ion-exchange particles) when coated on the filter media's surface. That is, the annular space serves as a free passageway for the particulates which is especially important when ion exchange resin particles and/or other particulate species are precoated onto the filter media. That is, the annular space allows such precoat particulates to move between the outer support cage and the pleated filter media surface such that the resin can form a uniform coating of resin over the media surface. Without the annular space, the particulates will preferentially coat the areas of the filter media exposed directly adjacent to the open void spaces of the solid outer protective cage. The areas under the solid portion of the outer protective cage will thus be coated nonuniformly. The particulates will also have the tendency in the absence of the annular space to cover the solid (non-apertured) portions of the outer support cage structure thereby resulting in nonuniform coverage. Less than optimum flow channels will result and inefficient use of the precoat particulates will occur.
In addition to the above advantages, the annular space allows the pleated media to radially expand thereby assisting in the release and removal of trapped particulates from the filter media's surface. This feature is especially important to allow the filter cartridge to be regenerated in situ with precoat particulates--that is, so that spent precoat particulates may be expelled from the filter media and again coated with fresh precoat particulates.
These and other aspects of the invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof which follow.